A conventional grinder has a driving unit mounted in the main body of the grinder. In the case of a pneumatic grinder, the driving unit is a pneumatic cylinder. In the case of an electric grinder, the driving unit is a motor. The driving unit serves to drive a rotary shaft to rotate. The rotary shaft is positioned at bottom end of the main body. In use, a grinding disc is connected with and driven by the rotary shaft for grinding or buffing an object.
In the conventional grinder, a gap exists between the grinding disc and the bottom end of the main body of the grinder. Therefore, the dirt, dusts and chips produced in grinding operation are easy to enter the interior of the grinder. Therefore, the internal components of the grinder tend to be contaminated. As a result, the function of the grinder will be affected. For example, in the case that the lubricant is polluted with the dirt, the quality of the lubricant will be deteriorated to reduce the lubrication effect between the components or even lead to clog of the components.